Article abstract
Nature Physics 2, 614 - 619 (2006)
doi:10.1038/nphys391
Subject Categories: Astrophysics | Particle physics
Cosmic-ray diffusion near the Bohm limit in the Cassiopeia A supernova remnant
M. D. Stage1, G. E. Allen2, J. C. Houck2 and J. E. Davis2
Abstract
The acceleration of cosmic rays in our Galaxy by means of diffusive shock (Fermi) acceleration is believed to occur primarily in supernova remnants (SNRs). Despite considerable theoretical work, the precise details are still unknown, in part because of the difficulty in directly observing nucleons that are accelerated to TeV energies in—and affect the structure of—SNR shocks. However, for the past ten years, X-ray observatories such as ASCA (Advanced Satellite for Cosmology and Astrophysics) and, more recently, Chandra, XMM-Newton and Suzaku, have made it possible to image the keV-scale synchrotron emission produced by cosmic-ray electrons accelerated in SNR shocks. Here, we describe a spatially resolved spectroscopic analysis of Chandra observations of the Galactic SNR Cassiopeia A to map the cutoff frequencies of electrons accelerated in the forward shock. We set upper limits on the diffusion coefficient and find locations where particles seem to be accelerated nearly as fast as theoretically possible (the Bohm limit).
- Five College Astronomy Department, University of Massachusetts, 710 North Pleasant Street, Amherst, Massachusetts 01003-9305, USA
- MIT, Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139-4307, USA
Correspondence to: M. D. Stage1 e-mail: mikstage@astro.umass.edu
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